Technical field
The present invention relates to partial discharge detection and acquisition system, and particularly, refers to partial discharge sensors.
Description of the Related Art
Partial discharge detection is particularly used for identifying and measuring partial discharges in electrical components and apparatus, such as: medium, high or extra-high voltage cables, cable joints, overhead line insulators, medium and high voltage switchboard boxes, high and extra-high voltage cables using GIS (Gas Insulated Switchgear).
The term partial discharges is intended to indicate an undesired recombination of electric charges occurring in the dielectric (insulating) material of electric components, when the latter have defects of various types, eventually leading to dielectric destruction. Here, a pulse current is generated in portions of dielectric material and causes an electromagnetic wave to propagate through the power or ground cables of the relevant electric system, and radiating through the various surrounding media (dielectric material, metals, air, etc.).
For executing partial discharge measurements on AC (Alternate Current) electrical components, a phase reference signal has to be detected, i.e. a signal that is synchronized in phase and frequency with the AC voltage powering of the AC electrical component.
The detected partial discharge signal and the phase reference signal are processed in an acquisition and analysis device which provides a representation of the detected partial discharge pulses with respect to the phase reference signal, allowing a final diagnosis of the electrical object under test.
Document WO-A-2009-150627 describes, inter alia, a partial discharge detection device of small size, totally insulated and self-powered, which allows measurements to be performed with the highest safety with no need for direct connection to the system under examination. This partial discharge detection device can also detect a synchronization signal, which is obtained by picking up the supply voltage of the discharge generating components.
Document EP0984289 describes a partial discharge detector for gas insulated apparatus (GIS), provided with an antenna unit, a coaxial cable and a remote measuring unit connected to the coaxial cable.
Document “Design and application of electric-field sensor for measuring PD signals in high voltage equipments”, K. W. Lee et al.; Proceedings of the International Conference of Properties and applications of Dielectric Materials June 1-5 2003—Nagoya, describes a partial discharge capacitor sensor comprising a first aluminium sheet connected to an input terminal and a second aluminium sheet connected to an output terminal and a polyester film placed between the two sheets. The described capacitor sensor, having a capacitance of about 1400 pF, shows a resonant frequency at 9.8 MHz.